Device for the automatic replacement and adjustment of tool carriers, more particularly angular milling heads on the milling support of a machine tool

ABSTRACT

A device for the automatic replacement and adjustment of tool carriers, such as angular milling heads on a milling support on a machine tool. A drawbar is axially slidably and rotatably mounted in the milling spindle. A base plate is provided for closing the milling support at the free end of the milling spindle. A tube is connected to the tool carrier and is secured to the free end of the drawbar. A fixing flange is provided on the tool carrier and extends parallel to the base plate. A fixing arrangement is provided between the fixing flange and the base plate for fixing the tool carrier in a predetermined angular position relative to the milling support. A plurality of clamping arrangements are mounted on the base plate and cooperate with the fixing flange.

llite tees Eicli et al.

1111 3,757,637 1 Sept. 11, 1973 [76] Inventors: Edmund Eicli,Sauerbruchstr. 8,

Coburg; Walter Muller, Schulstr. 8, Weitramsdorf; Bruno Fritsch, johLindun Str. 68lvt, Trenchtlingen, all of Germany 22 Filed: Sept. 13,1971 21 1 Appl. No.: 179,783

[30] Foreign Application Priority Data Sept. 15, 1970 Germany P 20 45604.6

[52] US. Cl. 90/17, 90/11 D [51] int. Cl 823d 1/12, 823d 9/00 [58] Fieldof Search 90/11 D, 17

[56] v References Cited UNITED STATES PATENTS 2,718,820 9/1955 Faselt90/17 2,307,222 l/l943 Johnson Kl/l7 Primary Examiner-Francis S. HusarAttorney-Woodhams, Blanchard & Flynn 57 ABSTRACT A device for theautomatic replacement and adjustment of tool carriers, such as angularmilling heads on a milling support on a machine tool. A drawbar isaxially slidably and rotatably mounted in the milling spindle. A baseplate is provided for closing the milling support at the free end of themilling spindle. A tube is connected to the tool carrier and is securedto the free end of the drawbar. A fixing flange is provided on the toolcarrier and extends parallel to the base plate. A fixing arrangement isprovided between the fixing flange and the base plate for fixing thetool carrier in a predetermined angular position relative to the millingsupport. A plurality of clamping arrangements are mounted on the baseplate and cooperate with the fixing flange.

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DEVICE FOR TllIE AUTOMATIC REPLACEMENT AND ADJUSTMENT F TOOLCARRIERS,-MORE PARTICULARLY ANGULAR MILLING HEADS ON THE MILLING SUPPORTOF A MACHINE TOOL The invention concerns a device for the automaticreplacement and adjustment of tool carriers, more particularly angularmilling heads on the milling support of a machine tool, having a drawbarmounted axially slidable and rotatable in the milling spindle andscrewthreaded on its free end, a base plate closing the milling supportat the free end of the milling spindle, a screwthreaded tube which isconnected to the tool carrier and in which the screwthread of thedrawbar is screwable, a fixing flange provided on the tool carrierparallel to the base plate, a fixing arrangement provided between thefixing flange and base plate and fixing the tool carrier inpredetermined angular positions relative to the milling support, anumber of clamping arrangements mounted on the base plate andco-operating with the flange, as well as a centring device betweenfixing flange and base plate. In modern machine tools, the tendency isto machine large workpieces in what is termed all-round machining, inwhich different machining operations are carried out on the workpiece inone setting. To enable this to be done, additional tool carriers suchas, for example, angular milling heads, spindle extensions and the likehave had to be temporarily attached. Economic use of such tool carriers,however, has been unsuccessful because the time required for mountingand dismounting, which was done by hand, was much longer than the actualmachining time. With hitherto known devices, therefore, it has not beenpossible to carry out machining economically and meet the requirementfor greater machining accuracy.

It is the object of the invention to provide a device for the automaticreplacement and adjustment of tool carriers, more particularly angularmilling heads on the milling support of a machine tool, whereby it ispossible to mount and dismount the tool carrier in a simple manner, in ashorter time and with greater accuracy.

The device according to the invention is characterized in that .a. thefixing arrangement is constructed in the manner of an indexingarrangement and is mounted on the outer periphery of the fixing flange,I

b. a motor-driven pinion is provided on the base plate and is rotatableabout an axis parallel to the milling spindle axis and meshes with atoothed crown connected to the fixing flange,

c. each clamping arrangement has a clamping pin hydraulically orpneumatically slidable parallel to the milling spindle axis and having ahead on its lower end engaging a corresponding annular T-slot of thefixing flange,

d. a control device is provided for the successive control of thedrawbar, pinion, fixing arrangement and clamping arrangement.

This new device makes it possible to lift the tool carrier automaticallyby means of the drawbar provided in the milling spindle and thescrewthreaded tube provided on the tool carrier, whereby the toolcarrier is centred and fixed. When this has been done, the tool carrieris rigidly connected to the milling support by the hydraulically orpneumatically operated clamping arrangement. By means of the newdevice,.the time spent in incidental operations in the machining of aworkpiece is shortened considerably, Servicing and manipulation of thetool carrier are simplified and facilitated. Whereas previously twopersons were necessary for mounting an angular milling head, this workcan now be done by one operator. Furthermore, in automatic mounting, therisk of accident is much less in comparison with manual mounting. It isalso possible to swivel the tool carrier automatically. This purpose isserved by the pinion driven by means of gearing and rotatable about anaxis parallel to the spindle axis, the said pinion meshing with atoothed crown connected to the fixing flange. In the various machiningoperations, it is necessary to swivel the angular milling head todifferent angular positions about the spindle axis relative to themilling support, additional small swivelling movements being necessaryfor the adjustment of the correct inclination (plunge) of the cutterhead relative to the surface to be machined. For this purpose, thefixing anrangement is constructed in the manner of an indexingarrangement, which permits fixing of the tool carrier in a number ofpredetermined angular positions relative to the milling support.

Further advantages and details of the invention are described moreparticularly in the following with reference to an embodiment exampleillustrated in the drawings, in which:

FIG. I shows a longitudinal section through the milling support andangular milling head with the new device in the position for mounting,

FIG. 2 shows a longitudinal section through these parts in the coupledposition,

FIG. 3 shows a horizontal section on the line Ill-III of FIG. 1,

FIG. 4 shows a part longitudinal section through base plate and fixingflange,

FIG. 5 shows a part cross section through part of the fixing device on alarger scale,

FIG. 6 shows an end view in the direction VI of FIG.

FIG. 7 shows an end view of one of the stops in the direction VII ofFIG. 3.

Referring to the drawings, at l is shown the milling support, in whichthe milling spindle 2 is rotatably mounted. Axially slidable androtatable inside the mill ing spindle 2 is the drawbar 3, adapted to beactuated by a driving motor 4, rotating together with the millingspindle. The drawbar 3 normally serves for gripping and releasing thetool shanks by means of a steep-angle cone and is known per se. The freeend of the drawbar is provided with a screwthread 5, which normally isscrewed into the tool shank before the actual axial movement of thedrawbar takes place by means of th motor 41.

An angular milling head 6 is shown in the ready position at the lowerend of the milling support I. This angular milling head is known per seand carries the cutter head 6a. On the upper end it has a fixing flange7 extending parallel to a base plate 23 closing the milling support.

Rigidly mounted on the angular milling head is a screwthreaded tube 14having at its upper end an internal screwthread 14a, into which thethread 5 of the drawbar 3 is screwable. Advantageously, a centring bush18, slidable against the force of the spring 19, may be mounted on thescrewthreaded tube 14. This centring bush 18 is provided with anexternal conicity or taper co-operating with the receiving cone 17 ofthe milling spindle 2.

During the coupling operation. the centring bush 18 serves to pre-centrethe screwthreaded tube 14 and to align the slots 15a, provided on thedriving shaft of the angular milling head 6, relative to the drivingblocks 16 on the milling spindle 2.

Alignment of the slots 15a and the driving blocks 16 is effected bymeans of the slots 18a in the collar of the centring bush 18, themilling spindle 2 being rotated until the driving blocks 16 engage theslots 18a, whereby the centring bush comes to bear against the internaltaper of the milling spindle.

Furthermore, there are provided on the base plate 23 a number, forexample four, hydraulically or pneumatically actuatable clampingarrangements S. Each of these clamping arrangements S has a clamping pin10 slidable parallel to the milling spindle axis and provided at one endwith a head 13 engaging a corresponding recess 8 of the fixing flange 7.The clamping pin is here loaded by springs, preferably cup springs, theentire clamping force being applied by the cup springs 12. For releasingthe clamping device, the other end of the clamping pin 10 is in the formof a double piston 11. The disengagement force acting against thesprings 12 is applied by means of high hydraulic pressure acting on thedouble piston 11, the clamping pins 10 being pushed downward.

To enable the angular milling head 6 to be swivelled about the spindleaxis relative to the milling support 1, the recess 8 is advantageouslyformed as an annular T- slot, provided with holes 9 at four points. Theholes 9 serves for the insertion of the heads 13 of the clamping pins10.

For exact centring of the annular milling head, a centring ring 20 isinserted and secured in the fixing flange 7. The centring ring 20co-operates with four ball rolling elements 22a spaced 90 apart in thebase plate 23. One such ball rolling element consists of a largeprincipal ball 22 and a number of small balls arranged in a ball bush,the principal ball 22 thus lying on a bed of small balls, capable ofrolling around the entire surface of a hardened steel sphericalsaucer-like dish.

Practically, therefore, a ball bearing is provided consisting of smallballs between the large ball and the spherical dish acting as support.The ball rolling elements are fitted radially in the base plate 23, sothat even in the case of a hot milling support and a cold angularmilling head they perform centring with sufficient preliminary stress,the expansion of the centring device produced by the heating of theangular milling head being taken up by the elastic deformation of thespherical bushes.

Advantageously, the centring ring 20 may also be provided with a toothedcrown 21 co-operating with a pinion 24, which is rotatable about an axisparallel to the spindle axis. To prevent the pinion 24 from beingdamaged during mounting, it may be slidable in the axial direction alongaxis 24A. The pinion is driven off an adjusting motor 26 through aeyclogear 27, an electromagnetic clutch 28, an electromagnetic brake 29and gearing 25. The control of the adjusting motor 26, electromagneticclutch 28 and electromagnetic brake 29 is produced by means of the limitswitches 32 and 39, described more particularly later.

In the case of angular milling heads, the latter must be fixed relativeto the milling support in certain angular positions around the spindleaxis. It is assumed that in the embodiment example shown, the angularmilling head is to be fixed in four positions spaced apart by 90. Forthis purpose, as fixing arrangement, four fixed stop bars 30 arearranged on the outer periphery of the flange 7, being spaced apart by90. Another stop bar 31 defines the position of the angular milling headon mounting and dismounting. Two rotatable stop pins 50 and 51 aremounted in the housing 23a rigidly secured to the base plate 23. Ontheir mutually facing ends, these stop pins 50 and 51 each have a stop33 and 34, respectively. These stops 33 and 34 co-operate with the stopbars 30, 31. To enable the angular milling head 6 to be swivelled, thestops 33,34 can be brought out of the path of movement of the stop bars30,31 by rotation of the stop pins 50,51 on their axes. For rotating thestop pins 50,51, the latter are each provided with a pinion 37,38meshing with a rack (only the rack 360 (FIG. 7) is illustrated) on eachof the pistons 35 and 36 which are adapted to slide transversely of thepins 50,51 by means of hydraulic pistons pressure. Whereas the stop pin50 with the stop 33 is immovable in the axial direction, the stop pin 51can be moved hydraulically in the direction A. A spring 52 is providedfor movement in the opposite direction. By the movement of the stop pin51 in the direction A, one of the stop bars 30,31 can always be clampedfast between the two stops 33,34, thereby fixing the angular millinghead in its angular position.

For plunge positioning of the cutter, the axially immovable stop 33 hasa number of different fixing positions, five in the example shown. Thesefixing positions are determined by axially offset stop faces 33a 33e.The middle stop face 33c is the zero position. The two adjacent stopfaces on either side 3311,3311 and $311,332 correspond to two plus orminus corrected positions. Rotation of the stop pin 50 on its axis bymeans of the hydraulic piston 36 brings one of the stop faces 33a 33einto the path of movement of the stop bars 30,31. The rotary position ofthe stop pin 50 is here determined by means of limit switches 40 to 44,adapted to be switched on from the control panel and co-operating with aswitch arm connected to the free end of the stop pin. The stop pinalways rotates until the switch arm has reached the limit switchswitched on from the control panel. In this way, one of the stop faces33a 33e is always used, whereby a greater or lesser angular variation isadjusted relative to the exact nominal angular position of the angularmilling head. By this means, an inclination of the cutting surface tothe workpiece surface to be machined is obtained. This plunge adjustmentis necessary for compensating a certain flexibility of the millingspindle in order to obtain optimum cutting conditions and surfacequality. The plunge adjust ment must be reversible in accordance withthe direction of the table movement, and for that reason the adjustmentof the stop 33, corrected according to plus or minus, has been provided.

The mode of operation of the new device is as follows: i

For mounting the angular milling head, the latter is set on the tableand brought into a position below the milling support such that themilling spindle and the screwthreaded tube 14 are more or less inalignment. By downward movement of the milling support, the millingspindle 2 is pushed over the screwthreaded tube. By switching on thedriving motor 4, the drawbar 3 together with the angular milling head 6is then drawn up until the driving blocks 16 bear against the collar ofthe centring bush 18, the centring cone 18 being pressed down againstthe spring. The milling motor is switched on and allows the millingspindle 2 to rotate slowly for a short time until the driving blocks 16engage the slots 18a in the collar of the centring cone 18. The drivingblocks 16 are then in line with the slots a in the driving shaft 15 ofthe angular milling head.

The centring bush l8 bears against the receiving cone 17, whereby mutualcentring of the parts is effected. The angular milling head is thendrawn up further by the drawbar 3, the centring ring 20 now comingbetween the balls 22 of the four radially arranged ball rolling elements22a and exact centring being accomplished. At the same time, the heads13 of the clamping pins 10 pass through the holes 9 in the annular slot8, the clamping pins being pressed down hydraulically against the forceof the spring 12. According to the desired angular position of theangular milling head 6, one of the limit switches 32 (FIG. 4) isswitched on at the control panel. Furthermore, by operation of one ofthe limit switches 40 44, the desired inclined position of the cutter ispreselected. Then, by means of the adjusting motor 26 and clutch 28, thepinion 24 is driven and the angular milling head is set in swivellingmovement. When a particular 90 position is reached, this is indicated bymeans of the switched-on limit switch 32, the adjusting motor 26 beingthereby switched off, the

clutch 28 is disengaged and the brake 29 is set in operation. The stopbar 30 concerned is then in the vicinity of or bearing against one ofthe stop faces 33a 33e corresponding to the preselected plunge position.By the action of the hydraulic piston 35, the stop 34 is swung into thepath of movement of the stop bar 30 and the stop pin 51 is shifted inthe direction A. The stop bar 30 is thereby pressed against the stopface 33a 33c switched on at the time and the angular milling head isthus fixed in the desired angular position. This having beenaccomplished, the pistons 11 of the clamping pins 10 are relieved ofload. The cup springs 12 move the clamping pins 10 upward and bringtheir heads 13 to bear in the annular T-slot 8. The angular milling headis thereby securely connected to the milling support, independentlyofexternal factors.

Swivelling of the angular milling head into another position can takeplace in a similar manner after release of the clamping pins andmovement of the stops 33,34 out of the path of movement of the stop bars30.

For dismounting the angular milling head, the stop bar 31 is brought tobear against the stop 33 by means of another limit switch 39 mounted inthe base plate. The clamping pins are then again in line with the holes9 and the angular milling head can be lowered by operation of thedrawbar 3. 1

The individual working operations necessary for the automatic mountingand dismounting of the tool carrier can be controlled and supervisedelectronically. Such electronic sequence controls are known in principleand therefore will not be discussed in greater detail here.

We claim:

l. in combination with a machine tool support having a rotatablespindle, an axially movable and rotatably movable drawbar mounted onsaid spindle and adapted for movement relative thereto between extendedand retracted positions, a base plate on said support extendinggenerally perpendicular to the axis of rotation of said spindle, toolcarrier means having a tool thereon and connecting means for connectingsaid tool carrier means to said drawbar for movement toward and awayfrom said base plate in response to extending and retracting movementsof said drawbar, said tool carrier means having a mounting flangethereon parallel to 1 said base plate when said connecting means couplessaid tool carrier means to said drawbar, adjusting and clampingapparatus, comprising:

indexing means for selectively fixing the position of said mountingflange relative to said base plate; rotary driven means for driving saidtool carrier means and said mounting flange for rotation about an axisparallel to said axis of rotation of said spindle between saidselectively fixed positions; and clamping means for clamping saidmounting flange to said base plate in one of said selectively fixedpositions.

2. The combination according to claim 1, wherein said indexing meansincludes indexing surfaces on said mounting flange and stop meanscooperable with said indexing surfaces, said stop means comprisingdriven stop members supported for movement into and out of the path ofmovement of said indexing surfaces.

3. The combination according to claim 2, wherein said rotary drivenmeans includes a driven pinion rotatable about an axis parallel to saidaxis of rotation of said spindle, gear teeth on said mounting flangeengageable with said driven pinion to drive said tool carrier means.

4. The combination according to claim 3, including means for supportingsaid driven pinion for movement in an axial direction.

5. The combination according to claim 3, wherein said driven pinionincludes an adjusting motor having an output shaft, an electromagneticclutch secured to said output shaft and a brake for controlling theoutput from said electromagnetic clutch.

6. The combination according to claim 3, wherein said clamping meanscomprises at least one clamping bolt supported for movement parallel tosaid axis of rotation of said spindle, said clamping bolt having anenlarged head thereon, said mounting flange having an annular invertedT-shaped groove therein having a vertical stern portion and a horizontalcrossbar portion and at least one enlarged portion adapted to receivesaid enlarged head on said bolt so that said enlarged head is movablebeneath the stem portion to said crossbar portion of said T-shapedgroove and subsequently out of communication with said enlarged portionof said slot upon a rotary movement of said mounting flange.

7. The combination according to claim 5, including limit switch meansfor controlling the operation of said adjusting motor in relation to theposition of said mounting flange to said base plate.

8. The combination according to claim 6, wherein said connecting meanscomprises first thread means on said drawbar and second thread means onsaid tool carrier means cooperable with said first thread means forcoupling said tool carrier means to said support.

9. The combination according to claim 8, wherein said tool carrier meansincludes a rotatably supported drive shaft for driving said tool;

wherein said second thread means is on said drive shaft.

10. The combination according to claim 9, including centering means forcentering said mounting flange relative to said base plate and saidspindle.

11. The combination according to claim 9, wherein said spindle ishollow; and

wherein said drive shaft has a centering sleeve mounted thereon foraxial movement against the force of a spring, said centering sleevehaving an outer conical surface thereon, said spindle having meansdefining a receiving cone on the interior thereof and is adapted toreceive said centering sleeve upon an axial movement of said drawbar.12. The combination according to claim 10, wherein said centering meanscomprises a centering ring on said mounting flange concentricallyarranged about the axis of rotation of said drive shaft and at leastthree ball elements mounted on said base plate concentrically about theaxis of said spindle, said ball elements being movable radially toaccommodate said centering ring therebetween to thereby center same withrespect to said axis of rotation of said spindle.

13. The combination according to claim 10, wherein said gear teeth areprovided on said centering ring which is fixedly connected to saidmounting flange.

14. The combination according to claim 2, wherein stop bolts includingprojections thereon for engaging said indexing surfaces, said projectionon said axially movable stop bolt being adapted to engage a projectionon mounting flange to push same against the projection on said secondstop bolt.

16. The combination according to claim 15, wherein said second bolt hasa plurality of axially offset surfaces thereon facing said first stopbolt, a plurality of limit switch means equal in number to said offsetsurfaces;

a switch arm secured to and rotatable with said second stop bolt andadapted to cooperate and actuate said limit switch means;

first drive means for rotating said second stop bolt and beingcontrolled by said limit switch means 0perable in response to saidswitch arm.

17. The combination according to claim 16, wherein said second stop bolthas a pinion thereon and rotatable therewith;

wherein said first drive means comprises a fluid operated piston havinga rack thereon engageable with said pinion and adaptedto rotate saidpinion upon an application of a fluid pressure to one side of saidpiston.

18. The combination according to claim 17, wherein said first stop bolthas a pinion thereon and rotatable therewith; and

including second drive means comprising a fluid operated second pistonhaving a rack thereon engageable with said pinion on said first stopbolt to rotate same upon an application of a fluid pressure to one sideof said second piston.

1. In combination with a machine tool support having a rotatablespindle, an axially movable and rotatably movable drawbar mounted onsaid spindle and adapted for movement relative thereto between extendedand retracted positions, a base plate on said support extendinggenerally perpendicular to the axis of rotation of said spindle, toolcarrier means having a tool thereon and connecting means for connectingsaid tool carrier means to said drawbar for movement toward and awayfrom said base plate in response to extending and retracting movementsof said drawbar, said tool carrier means having a mounting flangethereon parallel to said base plate when said connecting means couplessaid tool carrier means to said drawbar, adjusting and clampingapparatus, comprising: indexing means for selectively fixing theposition of said mounting flange relative to said base plate; rotarydriven means for driving said tool carrier means and said mountingflange for rotation about an axis parallel to said axis of rotation ofsaid spindle between said selectively fixed positions; and clampingmeans for clamping said mounting flange to said base plate in one ofsaid selectively fixed positions.
 2. The combination according to claim1, wherein said indexing means includes indexing surfaces on saidmounting flange and stop means cooperable with said indexing surfaces,said stop means comprising driven stop members supported for movementinto and out of the path of movement of said indexing surfaces.
 3. Thecombination according to claim 2, wherein said rotary driven meansincludes a driven pinion rotatable about an axis parallel to said axisof rotation of said spindle, gear teeTh on said mounting flangeengageable with said driven pinion to drive said tool carrier means. 4.The combination according to claim 3, including means for supportingsaid driven pinion for movement in an axial direction.
 5. Thecombination according to claim 3, wherein said driven pinion includes anadjusting motor having an output shaft, an electromagnetic clutchsecured to said output shaft and a brake for controlling the output fromsaid electromagnetic clutch.
 6. The combination according to claim 3,wherein said clamping means comprises at least one clamping boltsupported for movement parallel to said axis of rotation of saidspindle, said clamping bolt having an enlarged head thereon, saidmounting flange having an annular inverted T-shaped groove thereinhaving a vertical stem portion and a horizontal crossbar portion and atleast one enlarged portion adapted to receive said enlarged head on saidbolt so that said enlarged head is movable beneath the stem portion tosaid crossbar portion of said T-shaped groove and subsequently out ofcommunication with said enlarged portion of said slot upon a rotarymovement of said mounting flange.
 7. The combination according to claim5, including limit switch means for controlling the operation of saidadjusting motor in relation to the position of said mounting flange tosaid base plate.
 8. The combination according to claim 6, wherein saidconnecting means comprises first thread means on said drawbar and secondthread means on said tool carrier means cooperable with said firstthread means for coupling said tool carrier means to said support. 9.The combination according to claim 8, wherein said tool carrier meansincludes a rotatably supported drive shaft for driving said tool;wherein said second thread means is on said drive shaft.
 10. Thecombination according to claim 9, including centering means forcentering said mounting flange relative to said base plate and saidspindle.
 11. The combination according to claim 9, wherein said spindleis hollow; and wherein said drive shaft has a centering sleeve mountedthereon for axial movement against the force of a spring, said centeringsleeve having an outer conical surface thereon, said spindle havingmeans defining a receiving cone on the interior thereof and is adaptedto receive said centering sleeve upon an axial movement of said drawbar.12. The combination according to claim 10, wherein said centering meanscomprises a centering ring on said mounting flange concentricallyarranged about the axis of rotation of said drive shaft and at leastthree ball elements mounted on said base plate concentrically about theaxis of said spindle, said ball elements being movable radially toaccommodate said centering ring therebetween to thereby center same withrespect to said axis of rotation of said spindle.
 13. The combinationaccording to claim 10, wherein said gear teeth are provided on saidcentering ring which is fixedly connected to said mounting flange. 14.The combination according to claim 2, wherein said indexing surfaces aredefined by the laterally opposite sides of said projections extendingradially outwardly from said mounting flange; and wherein said stopmembers are adapted to engage said indexing surfaces to clamp saidprojections therebetween.
 15. The combination according to claim 14,wherein at least one of said stop members includes an axially movableand rotatable first stop bolt and axially fixed and rotatable secondstop bolt, said first and second stop bolts including projectionsthereon for engaging said indexing surfaces, said projection on saidaxially movable stop bolt being adapted to engage a projection onmounting flange to push same against the projection on said second stopbolt.
 16. The combination according to claim 15, wherein said secondbolt has a plurality of axially offset surfaces thereon facing saidfirst stop bolt, a plurality of limit switch means equal in number tosaid offset surfaceS; a switch arm secured to and rotatable with saidsecond stop bolt and adapted to cooperate and actuate said limit switchmeans; first drive means for rotating said second stop bolt and beingcontrolled by said limit switch means operable in response to saidswitch arm.
 17. The combination according to claim 16, wherein saidsecond stop bolt has a pinion thereon and rotatable therewith; whereinsaid first drive means comprises a fluid operated piston having a rackthereon engageable with said pinion and adapted to rotate said pinionupon an application of a fluid pressure to one side of said piston. 18.The combination according to claim 17, wherein said first stop bolt hasa pinion thereon and rotatable therewith; and including second drivemeans comprising a fluid operated second piston having a rack thereonengageable with said pinion on said first stop bolt to rotate same uponan application of a fluid pressure to one side of said second piston.